The point of this page is that the initial injustice of proprietary
software often leads to further injustices: malicious
functionalities.

Power corrupts, so the proprietary program's developer is tempted
to design the program to mistreat its users—that is, to make
it malware. (Malware means software whose functioning
mistreats the user.) Of course, the developer usually does not do
this out of malice, but rather to put the users at a disadvantage.
That does not make it any less nasty or more legitimate.

Yielding to that temptation has become ever more frequent; nowadays
it is standard practice. Modern proprietary software is software for
suckers!

Tyrants—systems
that reject any operating system not “authorized” by the
manufacturer.

Users of proprietary software are defenseless against these forms
of mistreatment. The way to avoid them is by insisting on
free
(freedom-respecting) software. Since free software is controlled
by its users, they have a pretty good defense against malicious
software functionality.